1. Field of the Invention
The present general inventive concept relates to an image forming apparatus in which a movable belt is movably installed to transfer an image formed on an image retainer to a printing medium.
2. Description of the Related Art
In general, an image forming apparatus, such as a laser color printer, includes an image retainer, such as a photoconductive drum, on which an image is developed, and a movable belt for transferring the image developed on the photoconductive drum to printing paper, namely, an intermediate transfer medium. Developing units for each color which sequentially develop Y, M, C and K color images on the photoconductive drum are installed around the photoconductive drum.
One example of the intermediate transfer medium is an intermediate transfer belt moving in contact with the photoconductive drum. Each color image is transferred from the photoconductive drum to the intermediate transfer belt in an overlapping type operation, so that the intermediate transfer belt can acquire a target color image. The final color image formed by overlapping is transmitted to a recording medium moving in contact with the intermediate transfer belt.
The intermediate transfer belt, supported by a plurality of supporting rollers including a driving roller and a tension roller, moves in one direction and transfers the overlap-transferred color image to the recording medium. The driving roller supplies power for moving the intermediate transfer belt, and the tension roller adjusts tension of the intermediate transfer belt. The length of the intermediate transfer belt eventually changes as a result of effects of the environment. Thus, the intermediate transfer belt can move under constant tension by adjusting the position of the tension roller.
On the other hand, while the intermediate transfer medium moves while supported by the driving roller and the tension roller, the intermediate transfer medium may shift to any one side due to mechanical errors of the supporting rollers. To solve the foregoing problem, guide rails are formed at both sides of the movable belt and both ends of the supporting rollers to support the movable belt. The guide rails formed at both sides of the movable belt prevent the movable belt from shifting to any one side along the axial directions of the supporting rollers, and guide the movable belt to move in a constant path.
However, when the guide rails are formed at both sides of the movable belt, a number of components increases to raise the unit cost of production.
To solve the above problem, there has been an attempt to reduce the number of the components and restrict shifting of the movable belt in side directions by forming the guide rail at one side of the movable belt. FIG. 1 is a schematic structure diagram illustrating a conventional movable belt disclosed under U.S. Pat. No. 5,017,969. Referring to FIG. 1, a guide groove 11 is formed at one end of a supporting roller 10, and the movable belt 20 supported by the supporting roller 10 includes a guide rib 21 corresponding to the guide groove 11. The guide rib 21 is inserted into the guide groove 11 to prevent the movable belt 20 from shifting in a B1 direction.
In the above structure, a number of components are reduced and shifting of the movable belt 20 in one direction B1 is prevented by forming the guide rail 11 and guide rib 21 at one side of the movable belt 20. However, it is difficult to restrict shifting of the movable belt 20 in another direction B2. That is, the movable belt 20 shifts in the B2 direction due to a sum force F3 of a tension F1 applied to the movable belt 20 by the supporting roller 10 and a control force F2 moving the movable belt 20 in the B2 direction by the guide rail 11 and guide rib 21.